1. Field of the Invention
The present invention relates to a method of fabricating an oxide thin-film transistor, and more particularly, to a method of fabricating an oxide thin-film transistor using an amorphous zinc oxide-based semiconductor as an active layer.
2. Description of the Related Art
In recent years, with rising interests in information displays and increasing demands to use portable information media, researches and commercialization of light-weight and thin-profile flat panel displays (FPDs) for substituting traditional displays such as cathode ray tubes (CRTs) have been actively carried out. In particular, among such FPDs, a liquid crystal display (LCD), which is a device displaying images using an optical anisotropy of liquid crystal molecules, has been actively applied to a notebook, a desktop monitor, or the like, because it is excellent in the resolution, color representation, image quality, and the like.
The liquid crystal display device is largely configured with a color filter substrate, an array substrate, and a liquid crystal layer formed between the color filter substrate and the array substrate.
An active matrix (AM) method, which is primarily used for the liquid crystal display device, is a method for driving liquid crystal molecules in a pixel portion thereof using an amorphous silicon thin-film transistor (a-Si TFT) as a switching element.
Hereinafter, the structure of a related art liquid crystal display device will be described with reference to FIG. 1.
FIG. 1 is an exploded perspective view schematically illustrating a related art liquid crystal display device.
As illustrated in the drawing, the liquid crystal display device may include a color filter substrate 5, an array substrate 10, and a liquid crystal layer 30 formed between the color filter substrate 5 and the array substrate 10.
The color filter substrate 5 may include a color filter (C) configured with a plurality of sub-color filters 7 for implementing red (R), green (G), and blue (B) colors, a black matrix 6 for dividing between the sub-color filters 7 and blocking light passing through the liquid crystal layer, and a transparent common electrode 8 for applying a voltage to the liquid crystal layer 30.
Furthermore, the array substrate 10 may include a plurality of gate lines 16 and data lines 17 arranged vertically and horizontally to define a plurality of pixel regions (P), thin-film transistors (T), which are switching elements formed at each crossing region of the gate lines 16 and the data lines 17, and pixel electrodes 18 formed on the pixel regions (P).
The color filter substrate 5 and the array substrate 10, as described above, are adhered by facing each other by a sealant (not shown) formed at an outside of the image display region to constitute a liquid crystal panel, and an adhesion between the color filter substrate 5 and the array substrate 10 is achieved by an alignment key (not shown) formed on the color filter substrate 5 or the array substrate 10.
However, the foregoing liquid crystal display device has been the most-spotlighted display element due to light-weight and low power consumption, the liquid crystal display device is not a light-emitting element but a light-receiving element and have technical restrictions in brightness, contrast ratio, viewing angle, and the like, and as a result, the development of new display elements for overcoming such disadvantages have been actively carried out.
An organic light-emitting diode (OLED) display, one of the new flat panel displays, is superior to the liquid crystal display in viewing angle, contrast ratio, and the like, because it is a spontaneous light-emitting type, and can be made light-weight and thin-profile and is advantageous in the aspect of power consumption because it requires no backlight. Furthermore, it is advantageous in driving a direct-current low-voltage and having a fast-response speed, and particularly advantageous in the aspect of the fabrication cost.
In recent years, studies on large-sized organic light-emitting displays have been actively carried out, and for the purpose of this application, it is required to develop a transistor for attaining a constant current characteristic in order to have stable operation and durability.
An amorphous silicon thin-film transistor used in the foregoing liquid crystal display device can be fabricated with low-temperature processes but has very low mobility and does not satisfy a constant current bias condition. On the contrary, a multi-crystalline silicon thin-film transistor has high mobility and a satisfactory constant current bias condition whereas it is difficult to make large-sized displays and also required to have high-temperature processes because it is difficult to attain a uniform characteristic.
Due to this, an oxide semiconductor thin-film transistor in which an active layer is formed with an oxide semiconductor has been developed, but it has a problem that the oxide semiconductor thin-film transistor may be damaged and transformed during an etching process of the source/drain electrodes thereof in case of applying the oxide semiconductor to a thin-film transistor having an existing bottom gate structure.
FIG. 2 is a cross-sectional view schematically illustrating the structure of a related art oxide thin-film transistor.
As illustrated in the drawing, a typical oxide thin-film transistor is formed with a gate electrode 21 and a gate insulation layer 15a on the substrate 10, and an active layer 24 made of an oxide semiconductor is formed on the gate insulation layer 15a. 
Subsequently, source/drain electrodes 22, 23 for electrically connecting to the source/drain regions of the active layer 24 are formed over the active layer 24.
At this time, the oxide semiconductor constituting the active layer 24 is deposited using a sputter, but during subsequent processes, a back channel region of the active layer 24 will be brought into contact with chemical materials during the photo process or exposed during the dry or wet etching and plasma processes, and the like, and thus the characteristics of the semiconductor thin-film may be changed, thereby deteriorating the element characteristics.
As described above, an oxide semiconductor has a weak coupling structure and thus an etch stopper 50 is additionally formed as a barrier layer over the active layer 24 to prevent the back channel region from being damaged by subsequent processes after depositing the oxide semiconductor, but it has a disadvantage of complicating the process as well as increasing the cost.
In other words, according to the related art, an active layer 24 is formed in the shape of an island through a photo process after depositing an oxide semiconductor and then an insulation layer for forming an etch stopper 50 is deposited. Then, through another photo process, the insulation layer is patterned to form an etch stopper 50.
At this time, since the patterning of the active layer 24 and the deposition of the insulation layer are progressed in a state that the vacuum of the vacuum chamber is released, the oxide semiconductor may be exposed to the air as well as brought into contact with chemical materials while being subject to the photo process, thereby causing the back channel region to be damaged. As a result, the element characteristics are deteriorated, and also a tact time is increased by the movement between chamber devices while depositing the insulation layer.